AVAILABILITY OF NITROGENOUS ORGANIC MATTER. 33 



10. Prom the results obtained, subtracting in each case 

 the amounts produced in the soil itself, calculate the per cent. 

 of organic nitrogen transformed to nitrate. 



11. Then taking the availability of (NHJ^SO, at 100 as 

 a basis, calculate' the relative availabilities of the other ma- 

 terials. 



12. Compare the results obtained in this experiment with 

 those secured in Exercise XIII., showing the comparative 

 availability indicated by ammonification and nitrification 

 tests. 



